Community Digest

Top new questions this week:

Which 8-bit computers were used in German schools in the 1980s?

In the 1980s, each country had a particular brand of computer that was most commonly used in schools; often, there was pressure to go with a local manufacturer. In the US, the Apple II. In Britain, ...

history commodore  
asked by rwallace 16 votes
answered by Raffzahn 19 votes

What are the difficulties in putting old AT style motherboards into modern ATX cases?

I have several 286, 386 and 486 motherboards that I would like to use. My problem is that while I have all of the components to make them functional, I don't have spare cases to put them in. ...

old-hardware-adaptation new-hardware-adaptation  
asked by cbmeeks 16 votes
answered by john_e 18 votes

Why did MC6809(E) require two-phase clock consisting of two square waves shifted by 90°?

Usually when talking about two-phase clocks in early CPUs, one means this type of clock, that consists of two non-overlapped pulses. Examples are MC6800 clock (page 3) or i8080 clock (page 6). Many ...

asked by lvd 15 votes
answered by Martin Maly 13 votes

History of ARM Linux and FPA

ARM Linux, at least Debian was traditionally (pre eabi) built for the FPA floating point unit*. Unfortunately under old ABI it was not easily possible to mix soft-float code with FPA code. The result ...

linux arm  
asked by Peter Green 13 votes
answered by Igor Skochinsky 5 votes

Looking for a 90s Macintosh game

I'm trying to find an early to mid 90s Macintosh game. It was a side scrolling shooter in the style of R Type. You flew a spaceship that looked vaguely like the USS Enterprise from Star Trek, albeit ...

apple-macintosh identify-this-game  
asked by hexamon 8 votes
answered by LаngLаngС 16 votes

NES chips usage

I am curently studying NES architecture to create a NES emulator. While looking up the NES motherboard schematics (, some of the chips usage are not clear to ...

emulation nes  
asked by Filipe Rodrigues 8 votes
answered by Curt J. Sampson 20 votes

What's the easiest way to bring up a MACLISP REPL on modern machines?

I'd like to bring up an old (pre-1975) LISP REPL so I can type things in and see how it behaves. MACLISP would be good but I'm open to other, similar LISPs, even as far back as LISP 1.5. What's the ...

asked by Curt J. Sampson 7 votes
answered by Curt J. Sampson 3 votes

Greatest hits from previous weeks:

Fixing obscure 8080 emulator bug?

I'm using the cpudiag.bin from to test my emulator. I've already implemented the CP/M CALL function at 0x05, offset the program at 0x100 and fixed the ...

asked by David Tran 37 votes
answered by George Phillips 94 votes

Why did the Apple IIe make a hideous noise if you inserted the disk upside down?

When I began high school in 1987 all the computers in the lab were Apple IIe desktop computers. A question has haunted me since then: if you inserted a floppy disk "upside down" the Apple IIe would ...

asked by Snack_Food_Termite 27 votes
answered by supercat 112 votes

Why did Unix use slash as the directory separator?

The Unix designers came from the GE/MIT Multics project, and Multics inspired some Unix features. In particular, Multics has a hierarchical filesystem, and so does Unix. On Multics, pathnames were of ...

unix multics  
asked by Barmar 65 votes
answered by Alex Hajnal 63 votes

Why was BASIC built into so many operating systems?

There are a lot of retro-computers with BASIC as an integral part of the operating system. The IBM 5100 was one of the first computers with a separate memory space for BASIC, followed by the Commodore ...

operating-system basic  
asked by wizzwizz4 81 votes
answered by blubberdiblub 68 votes

Why did computer video outputs go from digital to analog, then back to digital?

While early microcomputers used analog video outputs (often to use a television as a display), higher end machines such as the BBC Micro or Commodore 128 supported a digital RGB (or RGBI) video ...

history video display  
asked by Kaz 35 votes
answered by Martin Rosenau 5 votes

Were 9.2 file names possible in MS-DOS?

In MS-DOS (and FAT16), you could only have 8.3 file names (like QUESTION.TXT) with only single-case letters and numbers (and a few symbols). The MS-DOS Editor also defaulted to 8.3 - typing edit ...

asked by Zackary supports Monica 27 votes
answered by Alex Hajnal 127 votes

Why use static RAM addresses instead of the stack?

I'm studying the 65c816 assembly for the 1994 game, Super Metroid. A hobbyist studied the game in-depth and created a RAM map. From it: 7E:0B56 - 7E:0B57 Moves Samus this distance horizontally, ...

game-cartridge assembly snes  
asked by Andrew Cheong 52 votes
answered by pndc 53 votes

Can you answer these questions?

Apple IIe auxiliary RAM bank select register address -- C073 or C07X?

On the Apple IIe system, an "auxiliary RAM" card may be present which expands the built-in 64 kB RAM. When using an aux RAM card which has more than 64 kB, the auxiliary RAM bank in use can be ...

asked by Zane Kaminski 1 vote
answered by Raffzahn 0 votes

How much control of TRS-80 Model III disk drives was possible from its Cassette (ROM) BASIC?

How much control over the TRS-80 Model III's floppy drive controller can be effected via relatively simple commands, typed into its built-in Cassette BASIC? My understanding is that general usage of ...

basic trs-80 floppy-drive trs-80-model-iii  
asked by natevw 2 votes
answered by Raffzahn 0 votes

6502 interrupts when RDY is low

If the NMI line goes from high to low when the RDY is low, is the NMI detected, so that when RDY goes high, NMI is performed ? Or is the NMI discarded when it occurs when RDY is low ? (In case of ...

6502 interrupt  
asked by Johnmph 2 votes
answered by Raffzahn 0 votes
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